Surface Folds

Sulci, sharply creased surface folds, are found in soft materials like bread or an infant’s arm.

A sulcus is a sharply creased surface fold induced by compression in a soft material. It begins and grows like a crack, but is a continuous and reversible deformation. Sulci are found in primate brains and can be seen directly in a slice of bread (a) or in the arm of an infant (b), or indirectly as a disturbance pattern of glass dust on a folded and unfolded rubber slab (c) or as a pattern in refracted laser light passing through a folded rubber slab (d).